1. Field of the Invention
The present invention relates to a semiconductor integrated circuit device, and for example, relates to a system-on-chip (SoC) provided with an FM receiving function.
2. Description of the Related Art
Recently a composite wireless device in which plural wireless transceivers are combined has been widely used with the spread of various wireless systems. Not only a digital communication system but also an analog communication system are combined in the composite wireless system. An FM receiver can be cited as an example of the analog communication system. The FM receiver is used to receive an FM broadcast.
Frequently the conventional FM receiver has a circuit configuration in which FM wave detection is performed after a frequency of a received FM signal is converted into a first intermediate frequency and a second intermediate frequency with plural oscillators. On the other hand, recently there has been adopted a technique of setting the intermediate frequency at a low level in order to eliminate plural frequency selection filters. In this technique, after the frequency is downconverted into the intermediate-frequency signal, an analog-to-digital converter digitizes the intermediate-frequency signal, and a digital signal processor (DSP) performs signal processing to detect an FM wave. Therefore, the circuit scale of the FM receiver can be reduced, and the number of components therein decreased. The spread of the FM receiver having the above-described circuit configuration increasingly adds the FM receiver to an LSI (SoC) provided with a transceiver of another wireless system.
However, in cases where the FM receiver is incorporated in the SoC, noise becomes a major problem. Conventionally, many proposals have been made for the noise reduction of the single FM receiver. For example, Jpn. Pat. Appln. KOKAI Publication No. 2003-168991 discloses the noise reduction of the single FM receiver. However, unfortunately the noise reduction method adopted for the single FM receiver cannot deal with the noise in cases where the FM receiver is incorporated in the SoC.